#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>

int main()
{
	int money = 20;
	int count = 0;
	int empty = 0;
	count += money;
	empty = money;
	while (empty >= 2)
	{
		count += empty / 2;
		empty = empty / 2 + empty % 2;
	}
	printf("%d", count);
}
